The present disclosure relates to provision of an ancillary service for a power system, and particularly, to integrated energy storage using an electricity storage system and a frequency regulation technique.
For a certain given time, for example, for one day, an electric system operator estimates the amount of required energy per second, minute or hour.
An electricity provider supplies energy by as much as the estimated amount through a power plant. In general, an average actual load approximates to the estimated amount. However, the amount of required energy may change rapidly, and, if the amount of required energy becomes larger or smaller than expected, an actual load increases due to the rapid change in the energy amount.
To prepare for such a change, the electricity provider may change an electricity output from the power plant to meet a required load. Changing of the output from the power plant may be referred to as “load following”. In the case where a load is larger than transferred power, it would be obvious that the transferred power should be increased so as to maintain operation of electric devices.
FIG. 1 is a diagram illustrating an actual load 110 and load following 120 of a power plant. As shown, it is difficult for the power plant to accurately match a change in the actual load. In the case where supplied power differs from a power load, a frequency of AC current supplied to a home or a factory may not be 50 Hz or 60 Hz which may be referred to as a reference value. Such a frequency difference may cause inefficient operation of an electronic device such as a home appliance, a lighting device, or the like, and may even cause unsafe operation.
In order to maintain a required operating frequency of AC current, a power system operator should make the power plant perform an additional operation, i.e., frequency regulation. Referring to FIG. 1, reference numeral 130 represents how frequently the frequency regulation should be performed for each moment in order to maintain a frequency within a desired operating range.
When a (required amount of) load is smaller than supplied power, an output frequency increases to 60 Hz or higher. On the contrary, when the load is larger than the supplied power, the frequency decreases since an energy generation amount of a power plant decreases.
The idea of providing a fast-response power plant synchronized with a frequency of a system or a fast-response power plant capable of quickly starting to supply energy in response to a failure event or other problems pertaining to power supply may be conceived of. However, it is currently difficult to configure such a power plant.
In general, services such as a synchronous storage and frequency regulation are classified as ancillary services for a power system. Such services should satisfy the requirements of energy for power provision and consumption.
The frequency regulation, synchronous storage, and other ancillary services are provided by a power plant. However, an energy storage technology such as a battery, a flywheel, a capacitor, or the like may be used to supply energy to an electric power system. Furthermore, according to such energy storage technologies, surplus energy of the system may be stored for later use or may be discharged from the system.
Since the frequency regulation should be performed to increase or decrease energy so as to maintain a constant energy amount of a system for each moment (reference numeral 130 of FIG. 1), an energy storage technology is required to satisfy such a requirement.
An energy storage technology may represent a technology for improving the efficiency in use of energy generated by a power plant, instead of generating energy. The efficiency may represent a lower cost and a lower rate of energy discharge in terms of operation of a power system.